1. Field of the Invention
The present invention relates to a color xerographic copier and more particularly relates to a multi-mode color copier having raster input and output scanning capabilities.
2. Prior Art
Color copiers are known in the art. U.S. Pat. No. 4,135,927 entitled "Multi-Color Xerographic Process" to Draugelis et al. discloses one such color copier. According to the copying techniques disclosed in the '927 patent, a charged photoconductive member is sequentially exposed to a series of color separations of a color original in order to form a plurality of latent electrostatic images. As disclosed in the '927 patent this separation is achieved by transmitting the original image through a number of filters which selectively transmit colors to the photoreceptor. Each color separated image is then developed with a complementary toner material, i.e., a developer material containing a colorant which is a substractive complement of the color transmitted through the filter. The developed image is then transferred to a copy substrate and the photoconductive member cleaned. The colored original is then again optically imaging using a different filter, developed using that filter's complementary toner and then transferred to the copy substrate. Once all primary colors have been separated and brought together on a sheet of support material, the colored toner materials are fused. This above-defined process is similar to conventional xerography since developed images are physically transferred from a developed photoconductor to a copy substrate.
Raster input scanning and raster output scanning are two modifications to conventional xerography which heretofore have not been readily adapted to color copying. Raster output scanning (ROS) involves the line by line scanning of a charged photoreceptor to encode or write information onto that photoreceptor. ROS techniques typically involve modulation of a laser output in a controlled manner to encode this information. The laser is selectively turned on and off as its beam traverses across a charged photoreceptor in a controlled manner so that selected portions of the photoreceptor can be discharged and certain other portions remain charged.
In so called raster input scanning (RIS) a scanning technique is used to read information using a laser beam. According to this technique, a laser beam is selectively scanned across a document so that photodiodes optically coupled to the document will be selectively illuminated by the document. Techniques are known in the art for then translating the output from the photodiodes into information corresponding to the information content of the scanned document. This information can be stored or directly coupled to a ROS system for writing the information with a ROS system.
Copending U.S. patent application Ser. No. 111,520 entitled "Multiple Function Reproduction Apparatus" to Kramer et al. discloses a multi-function copying system incorporating both RIS and ROS systems. In a first mode of operation the apparatus disclosed in that application functions as a conventional copier wherein an image of a document original is transferred to a photoreceptor, a latent image is developed and transferred to a copy sheet for subsequent fusing. In a second mode of operation a flying spot laser beam writes images on a charged photoconductive surface in response to imaging signals input to that system. In this mode of operation, the beam impinges on the photoconductive surface at a location upstream of a developing system so that the encoded information from the laser beam can be developed and subsequently transferred to a copy sheet. In a third so called read mode of operation a beam impinges on the photoconductive surface downstream from the developing device to scan images developed on the photoconductive surface. The light scattered from the surface is collected and converted to image signals representative of the image so scanned. This last, read mode of operation corresponds to conventional RIS scanning. Rather than scanning a document, however, the RIS technique is utilized to scan a developed photoreceptor image so that all three xerographic functions can be performed using a single apparatus.